In an ene-thiol based photocurable resin composition which is a radical polymerization type photocuring system, active thiyl radicals are regenerated even when radicals are deactivated by oxygen. Said composition therefore has advantages such that polymerization inhibition caused by oxygen that occurs in acrylic materials does not occur, that the used amount of a photopolymerization initiator can be reduced, that volume shrinkage at the time of curing can be reduced, that curing can be done in a short period of time, i.e., from a few seconds to a few minutes after the initiation of polymerization, and that cured products of thick-film having a thickness of 1 mm or more can be produced, and is gathering attention as a photocurable material (Non-Patent Document 1).
For example, Patent Document 1 discloses a photocurable resin composition comprising polyene, polythiol and a compound having a bromine-substituted aromatic ring having a specific structure, in which the mass ratio of the polyene to the polythiol is from 49:1 to 1:49, as such an ene-thiol-based photocurable resin composition. Also, Patent Document 2 discloses an ene-thiol-based photocurable resin composition comprising a polyene compound, and a (poly)thiol-based monomer consisting of a reaction product of a polyvalent amine compound and a mercaptocarboxylic acid compound.
The technology disclosed in Patent Document 1 provides a photocurable resin composition having a high refractive index, in which the refractive index can be adjusted with high precision. The technology disclosed in Patent Document 2 provides a cured product that can be cured in a short period of time without polymerization inhibition caused by oxygen and with reduced volume shrinkage, and in which the amount of a photopolymerization initiator used can be reduced and humidity resistance is notably improved. However, Patent Documents 1 and 2 do not in any way mention the shock absorption and vibration absorption of the cured product.
Patent Document 3 discloses a transparent resin consisting of a cured product of a polymerizable composition comprising at least one of diallyl phthalate, diallyl isophthalate and diallyl terephthalate, and pentaerythritol tetra(3-mercaptopropionate). However, the concept of the shock properties described in Patent Document 3 which concern penetration of a ball and scattering of a sample is close to that of toughness and elongation properties, which are different from shock absorption in terms of rebound properties. Also, there is no mention of turbidity (haze) and yellowing (b* value) which indicate transparency.